Usually the people listed in your Contacts list are regarded as safe by Outlook’s Junk E-mail Filter.  Usually being the key word.  I ran into an instance today where an interoffice email sent went into the recipients Junk Folder.  To correct this I used the following steps.

Go to Tools Options

The Preferences tab should be selected by default and click on the Junk E-mail button.

From here click the Safe Senders tab and verify a check in the box next to Also trust e-mail from my Contacts.  I also check Automatically add people I e-mail to the Safe Senders List, though you will want to be cautious with this one and may want to turn it off if you start getting SPAM.